Cutting implements have been used for many years. Most cut by shearing action. Scissors are typical. To cut using scissors, the blades are positioned on opposite sides of the material, and the blades are then pressed together with enough force to drive the blades through the material to be cut. The material is cut or, more accurately, separated, by the shearing action of the blades as they move through the material.
Scissors have several drawbacks, one of which is that they are not safe. The exposed blades of a scissors can cut the user and, if dropped, the generally pointed edges can cause puncture wounds. They can be difficult to pick up as the handles, to which the blades are connected, are free to rotate about a central pivot. Additionally, the length of a cut that can be obtained using conventional scissors is limited to the length of the blade which is employed. Cuts that are longer than the length of the scissors blades are frequently ragged, as the stop and start point for each cut is generally clearly visible.
For people who use scissors frequently, carpel tunnel syndrome may become a problem. Carpel tunnel syndrome is an inflammatory condition that may be caused by overuse of the muscles or connective cartilage of the wrist, a condition that accompanies the frequent use of scissors.
A razor blade is another type of cutting device frequently used for some types of cutting. The danger inherent in using a razor blade or an equivalent sharp edged instrument, such as a knife, is well known. While they provide the ability to cut continuously, they dull quickly, will often rip and ruin the material as the blade dulls, and are quite capable of maiming or destroying fingers, hands and other parts of the human anatomy. If the material to be cut is placed on a substrate, or is a cardboard shipping container, the razor blade or knife will also tend to cut the substrate or the product contained in the cardboard container.
Another type of cutting device has been employed which contains a pair of ball bearings mounted in tandem, with the axis of each ball bearing offset vertically from the other. This device is described in Hungarian Patent No. 179232. In addition, a cutting implement that employs a pair of ball bearings has been commercially available on the market in the United States.
In connection with the aforesaid commercially available twin ball bearing cutting implement, one of the ball bearings is mounted on a plastic non-rotatable shaft that is in turn located on the main body of the device, which is also made of plastic. The second ball bearing is mounted on a separate plastic carrier containing a second non-rotatable shaft made of plastic, and the carrier is connected to the main body by means of glue and a single small screw. The carrier is also provided with one or more locating dowels which are received in receiving holes provided in the main body of the device. Glue is employed to retain the dowels in the receiving holes. The plastic employed in this device is of the nylon family, which we have found tends to absorb moisture and swell. If moisture is absorbed by the plastic, it tends to change the dimensional relationship between the ball bearings when the ambient humidity is high, thus tending to destroy the cutting ability of the device.
Cutting forces that act on the opposed bearings resolve into opposed radial forces that tend to cause the ball bearings to separate in the radial direction, and opposed axial forces, which tend to cause the ball bearings to separate in the axial direction. Applied forces generated in ordinary cutting activities are frequently sufficient to cause the glue connection between the plastic carrier and the plastic main body to shift or to completely separate, thus causing the ball bearings to lose contact with each other. The frequent result is a permanent realignment of the relationship between the ball bearings. When this occurs, the device will no longer be able to cut. We have observed that the carrier will permanently shift, with consequent permanent realignment of the ball bearings, with loads applied by attempting to cut several sheets of copy or bond paper at one time, or by attempting to cut any relatively thick sheet of material, such as thin cardboard, poster board and the like. One result is that the prior art device is limited to thin materials, generally less than 0.4 mm in thickness (stated on its packaging), and will not absorb much force and still retain its ability to cut.
In addition to the foregoing, the prior art device would frequently not work to cut material after it had been assembled, regardless of the level of the force applied to the ball bearings. To make these useful, adjustments were required, which generally took the form of adjusting the screw used to mount the ball bearings to their respective shafts to either move the ball bearings closer to each other, or farther apart to reduce the force of contact between the two ball bearings. However, any misalignment of the bearings that occurred during cutting would render the unit unusable.
Still further, the prior art construction frequently failed to establish a contact point at the point of entry of the material to be cut. If a contact point was accidentally established, it was frequently established at the wrong location. The knowledge required to repeatedly make useful devices was not displayed by the prior art devices. Making these prior art devices useful was a matter of luck and experiment rather than design. The reject rate, even after such experimentation, remained substantial.